Flexibility degrades strength?

I've actually heard this a few times, from varying levels of martial artists from different diciplines.

The basic idea is when you do the "static stretching" (such as the classic leg spread eagle), your tendons get overextended and get weakened.
Their alternative solution is "dynamic stretching". Now, people's thought on how this should be performed is different. Some people say it should be done like aerobics, and some even say "just try to kick high until your tendos naturally stretch".

This sounds like a slightly garbled account of one version of conventional wisdom regarding stretching, which goes more like this:

You should not do static stretching ahead of a workout, because it may weaken your muscles slightly and, in some studies, correlates with an increased risk of injury. Instead, a pre-workout routine should consist of a warmup (raising your core temperature) and light dynamic stretching, which warms up the muscles. After your workout, it’s a good idea to do some static stretching to maintain and/or improve flexibility.

In other words, it’s not that you shouldn’t do static stretching, it’s that you shouldn’t do static stretching before a workout.

Now, in citing this as conventional wisdom, it is of course one massive [citation needed]. It is the version I myself subscribe to, mostly because discussions around here where evidence was cited were fairly convincing. If you use the search function, you’re likely to find more.

Does static stretching reduce a muscle's force output? Yes, temporarily. This doesn't happen because the tendons are getting weakened (stretches that involve muscles will never really stretch a tendon. Tendons are rigid by necessity to transfer the force muscles produce, whereas the muscles are very flexible. Thus, any stretching force is going to take the path of least resistance: the muscle tissue). It happens because prolonged static stretching tells the nervous system to signal that muscle to relax and reduce its tension production. But this effect is only temporary.

Is this bad? It can be, it can be good. If you're engaging in an intense strength or power workout, there is a significant chance your abilities will be reduced by significant static stretching immediately beforehand. However, if you have postural instabilities where a chronically tight muscle is affecting your movement patterns, then it might be a good idea. The stretching beforehand will temporarily reduce the chronic tension in that muscle, which will ideally minimize its negative effect on your quality of movement.

Responding specifically to the thread title: Flexibility (as in the physical attribute, separate from stretching as an activity) itself does not degrade strength in any regard. It might even have a slight benefit to strength. But most likely, it will not affect strength in either direction. Muscles themselves are ridiculously flexible in their natural state. Most muscles can actually extend 2-3 times their resting length without tearing, if there were no other factors involved (i.e. if the muscle were removed from the body). There are a large number of factors to flexibility that result in a person's ultimate range of motion.

But really, flexibility and strength reinforce one another. You can have both together, and you should. One without the other only means you're missing out on physical attributes you could be having.

Petter -- I believe the research you are talking about in terms of stretching reducing force output has been either produced by or cited frequently by Stuart McGill. The name comes up fairly frequently in those discussions anyhow, so if anyone cares to be a source checker, go for it.

I can't recall if it was either a lab or case study, but I do think there was a contradictory study which stated that static stretching followed by a dynamic warm-up produced near identical results in performance to just a dynamic warm-up. I can't remember who the source is on that one either so it's also possibly just anecdotal.

I'm pretty much entirely on the same page as Taebo, but would like to tack on a slight addition.

There is such a thing as too much flexibility. In the extremes this results in instability if there is not sufficient strength to maintain or stabilize the joint position. In that way strength and flexibility can be opposites of sorts, but in many ways they are complimentary.

A quick example that comes to mind would be to imagine someone with chronically tight hamstrings. If this person goes to do a leg extension machine, the end range of motion is going to be highly restricted by the tight hamstrings making it WAY harder if not impossible to achieve a full/end range quadraceps contraction. The leg extension usually sucks, for the record.

Depends on what the source of that extreme flexibility. Typically, even extreme flexibility developed in an "athletic" manner (meaning by deliberate training) is unlikely to result in joint laxity. Usually, this is the result of congenital or incidental factors that reduce the ability of the ligaments to maintain the joint capsule. Incidental factors could include an injury that damages the ligaments (seen often in dislocated shoulders), or biological ones.

The only people I have met who are more flexible than Olympic weightlifters are gymnasts and contortionists.

Calm down, it's only ones and zeros.

"Your calm and professional manner of response is really draining all the fun out of this. Can you reply more like Dr. Fagbot or something? Call me some names, mention some sand in my vagina or something of the sort. You can't expect me to come up with reasonable arguments man!" -- MaverickZ

This sounds like a slightly garbled account of one version of conventional wisdom regarding stretching, which goes more like this:

You should not do static stretching ahead of a workout, because it may weaken your muscles slightly and, in some studies, correlates with an increased risk of injury. Instead, a pre-workout routine should consist of a warmup (raising your core temperature) and light dynamic stretching, which warms up the muscles. After your workout, it’s a good idea to do some static stretching to maintain and/or improve flexibility.

In other words, it’s not that you shouldn’t do static stretching, it’s that you shouldn’t do static stretching before a workout.

Now, in citing this as conventional wisdom, it is of course one massive [citation needed]. It is the version I myself subscribe to, mostly because discussions around here where evidence was cited were fairly convincing. If you use the search function, you’re likely to find more.

This.

There were some studies done in Sweden (I believe) a few years back that showed static stretching before weightlifting increased the potential for injury.